Donald Trump Wows at First Solo Stress ConferenceCredit...CreditVideo by "The Late Show With Stephen Colbert"

The president’s conference “was a robust one hour and 17 minutes long,” said Mr. Colbert in the “Late Show” monologue that night. “It was so beefy you could eat it with a fork. But you’re going to want to use a spoon to get every drop of the crazy.” He played a clip in which Mr. Trump declared, “I inherited a mess.” Mr. Colbert answered: “No, you inherited a fortune. We elected a mess.”

Mr. Fallon began NBC’s “The Tonight Show” in bronzeface as Mr. Trump, squinting and head-bobbing, hitting many of the same highlights, but much less pointedly. “We inherited a mess,” he said. “It is such a mess. Not even a giant Roomba could clean it up.” Drinking from a water glass held in a tiny prop hand, he added: “I’ve just made my new secretary of labor Beyoncé. Who knows more about going into labor than someone carrying twins?”

When Mr. Colbert moved to CBS from Comedy Central a year and a half ago, he was the one struggling to adjust. How could he transition from the scathing political comedy of “The Colbert Report” to broadcast TV, where Mr. Fallon had shown, like Jay Leno before him, that audiences just want to escape after a long day?

Mr. Trump has upended that dynamic the way he has so many others. Since his inauguration, there’s no escape. And there’s surprisingly little ratings evidence that people are looking for one. “Late Show” has begun beating “Tonight” in overall viewers. And it’s Mr. Fallon who’s navigating a suddenly foreign environment.

Mr. Colbert is not, right now, the fiercest of the late-night anti-Trumpists (that’s Samantha Bee), the most depthful (John Oliver) or the most potent (Seth Meyers, whose “A Closer Look” segments are killing). But he has a bigger stage, and he seems to have figured out how to be authentic within that space.

This was a process: The early months of his show were fitfully topical but tentative, as Mr. Colbert tried to find a voice without the filter of his arch fake-pundit character. His live shows during the 2016 conventions were a creative turning point. But the philosophical turning point may have been on election night, when Mr. Colbert hosted a live special on Showtime.

It was both one of the worst and one of the best shows Mr. Colbert has ever done, growing both awkward and earnest as it sunk in, live on camera, that Mr. Trump would be the next president. “I can’t put a happy face on that,” he said, “and that’s my job.”

Instead, he has put his game face on. Mr. Colbert’s comedy hasn’t become radically different, but it has been more frank and caustic. After the president implied that something dire had just taken place in Sweden (it hadn’t), on Monday night he quoted former Prime Minister Carl Bildt of Sweden, who asked, “What has he been smoking?” Mr. Colbert suggested a certain part of the Russian president Vladimir Putin’s anatomy.

Then he smiled, walked to the camera and blew a kiss. The network-TV Mr. Colbert is more cheery than his cable character. But it’s as if the Trump administration had solved the problem of reconciling his new comedy with his old by making truthiness America’s official language.

Some of Mr. Colbert’s deadpan jokes on the Sweden story — “Never Fjorget” — could have come straight off the “Report”: “Tragically, Sweden is the third not-a-terrorist-attack that has not shocked the world in the last month. First, there wasn’t the Bowling Green Massacre, then no one was lost in Atlanta.”

Mr. Colbert’s ability to do more serious interviews — minus the ironic distancing of his “Report” character — has also been an advantage. On Tuesday, Joe Scarborough, the Republican host of “Morning Joe,” told him that his party colleagues “are going to be judged for the next 50 years” on how they respond to Mr. Trump’s attacks on the press and the judiciary. (“I wish I shared your optimism that there will be a time after Donald Trump,” Mr. Colbert said.)

Mr. Colbert’s and Mr. Fallon’s approach to Mr. Trump’s presidency is, broadly: “This is crazy.” But where Mr. Colbert means it in the sense of, “This is terrifying,” for Mr. Fallon it’s more like, “This is silly.”

His “Tonight” monologues about Mr. Trump have been quick and glancing — but Mr. Fallon has never really been a monologue guy. He has played Mr. Trump as the anchor of his own news network (“100 percent fair and 112 percent factual”), and in the Oval Office spinning a wheel with the names of potential Supreme Court nominees while dancing to the “Price Is Right” theme song. He has goaded Alec Baldwin, the “Saturday Night Live” impressionist in chief, into a battle of Trumps.

His bits have been typical Fallon — goofy, light, full of pop culture references. But right now, they feel the opposite of huge.

Mr. Fallon has seemed to be behind the cultural moment at least since September, when he invited Mr. Trump onto his show to fluff his combover. To Mr. Fallon’s critics, it was “normalizing,” which has become a buzzword for any insufficiently zealous response to Mr. Trump’s presidency.

It’s a pretty accurate word for Mr. Fallon’s approach, though. That’s not to say he has any deliberate plan to soften Mr. Trump’s image. (In fairness, he also had Barack Obama on for “Slow Jam the News.”)

Rather, the whole spirit of Mr. Fallon’s comedy is that of someone who badly wants things to just be normal again. Guys! Can we all cool off and laugh about the president’s goofy hair? Can’t we just take an hour and chill?

But things aren’t normal. Not even Mr. Trump’s fans — who voted for him to deliver a shock to the system — see it that way. Mr. Trump made his campaign angry, cultural and personal. As president, he has continued to goad his followers into a war of all against all with internal enemies: refugees, the media, any Americans deemed less “real.”

Mr. Trump prods for response, and he gets it — at awards shows, on your Facebook feed, in Super Bowl ads, in N.B.A.-coach press statements. Mr. Fallon is a talented entertainer and a likable, inclusive party host. But his “Tonight” lives in an American neutral zone that is disintegrating like a desert cliff beneath Wile E. Coyote’s feet.

Very recently, Mr. Fallon’s political material has gotten a bit feistier. After Mr. Trump visited the National Museum of African American History and Culture on Tuesday, he joked, “Things got awkward at each exhibit when Trump would turn to Ben Carson and say, ‘Friend of yours?’”

But most of “Tonight” is still a retreat from the all-Trump mediasphere. That’s Mr. Fallon being Mr. Fallon, doing the same energetic, upbeat show he’s good at doing. Only now it feels like a plaintive holdover from a distant, more innocent time — like 2015.